CDJ-2000NXS2 Cannot deactivate Master Tempo

Hello. I just bought a second-hand CDJ-2000NXS2 is stuck in "Master Tempo" mode and I can't turn it off. When I click the Master Tempo button it switches "Tempo Reset" on and off (including the corresponding green LED in the middle of the tempo fader).

Is this a feature or a bug? And how do I fix it?

The unit is in overall great condition but this is the only thing I can't work out.

Thank you!